1. Field of the Invention
The present invention relates generally to circuits for station scan functionality in a radio receiver. More specifically, the present invention relates to techniques for conducting a station scan in a digital receiver.
2. Description of the Related Art
In a given geographic area, numerous stations may be broadcasting radio frequency (RF) signals on different channels. These RF signals may be AM or FM signals and may include desired program information. A radio receiver present within this geographic area, either fixed or mobile, will attempt to receive and recover the program information being broadcast by the stations. Often it is desirable for the radio receiver to have the ability to scan for the presence of stations in the geographic area. For example, when a person is traveling in an automobile through an unfamiliar geographic area, that person will likely not know the channels on which stations are broadcasting program information. Such station scan to capabilities, however, often require a radio receiver to include additional circuitry that may add undesirable costs and complexity to the radio receiver.
In accordance with the present invention, station scan circuitry efficiently determines the presence of a station on available channels. Channels are analyzed to determine if the signal power on a given channel exceeds a threshold value. A comparison is also made between the desired channel signal strength and the adjacent channel signal strength. If the signal power and the ratio of signal strengths exceed selected threshold levels, the station scan circuitry indicates that a station has been found. To make the signal strength ratio comparison, the station scan circuitry makes a comparison of the post-filter signal strength and the pre-filter signal strength for the received signal.